Recently, alcohol-blended gasoline is used as fuel of vehicles in order to protect the environment. In this case, it is necessary to set an appropriate fuel injection amount and an ignition time based on a mixed ratio of the alcohol in the gasoline. Thus, in the vehicles, a sensor is generally provided so as to detect the mixed ratio of the alcohol to the gasoline. For example, in U.S. Pat. No. 7,030,629, an electrical characteristic of a fluid is measured so as to detect a fluid property, and the detected value is corrected based on a fluid temperature, thereby improving the detecting accuracy.
In the sensor described in U.S. Pat. No. 7,030,629, the electrical characteristic of the fluid to be detected is detected by using an electrode portion exposed to the fluid, and then the fluid property is determined based on the detected value and a fluid temperature measured by a temperature sensor via the electrode portion. The electrode portion and the temperature sensor are held inside of a housing exposed to the atmosphere. Therefore, heat is transmitted from the atmosphere via the housing, and thereby it is difficult to accurately measure the fuel temperature. When the fluid temperature cannot be accurately measured, the fluid property cannot be accurately detected.
In a fuel property sensor described in JP 1-163862U, an electrode portion is configured to have a hollow structure, and a temperature sensor is accommodated in the electrode portion. Thus, the temperature sensor can detect the temperature of the fuel without receiving heat from the atmosphere.
In the fuel property sensor described in JP 1-163862U, a sensing portion at a tip end of the temperature sensor is made to contact an inner wall of the electrode portion. Thus, if a dimension difference is caused in the electrode portion or the temperature sensor, it may difficult for the sensing portion to accurately contact the inner wall of the electrode portion, and thereby it may difficult to accurately measure the fuel temperature by using the temperature sensor. Furthermore, because the coefficient of linear expansion is generally different between the electrode portion and the temperature sensor, a stress may be applied to a conductive wire of the temperature sensor fixed to a substrate, and thereby the conductive wire of the temperature sensor may be damaged.